Method for controlling fuel cell device

ABSTRACT

A method of controlling a fuel cell device includes: a step of supplying hydrogen to a hydrogen supply unit; a step of measuring a voltage between a fuel electrode and an oxidant electrode and determining whether the voltage is equal to or greater than a reference voltage; and a step of discharging a gas containing oxygen from the gas supply unit to the outside while supplying the gas to the gas supply unit when the voltage is equal to or greater than the reference voltage.

TECHNICAL FIELD

The present invention relates to a method of controlling a fuel celldevice and, in particular, to a method of controlling a fuel cell deviceduring a steady operation.

Priority is claimed on Japanese Patent Application No. 2020-024701,filed Feb. 17, 2020, the content of which is incorporated herein byreference.

BACKGROUND ART

Fuel cells are devices that directly convert chemical energy of fuelsinto electrical energy by causing fuels such as hydrogen to react withoxidants such as air (oxygen) electrochemically. Among fuel cells, solidpolymer electrolyte fuel cells in which hydrogen ion-exchanged polymermembranes or the like are used in electrolytes have excellentcharacteristics of high output density, simple structures, andrelatively low operation temperatures. Therefore, development of varioustechnologies for fuel cells which can be mounted on mobile objects suchas airplanes or vehicles is in progress.

As fuel cells of the related art, a fuel cell that generates power usinghydrogen gas supplied to a fuel gas flow passage and an oxidant gassupplied to an oxidant gas flow passage and a fuel cell that includes afuel supply system supplying a fuel to a fuel gas flow passage, anoxidant supply system supplying an oxidant to an oxidant gas flowpassage, and fuel supply means for selectively supplying a fuel to theoxidant gas flow passage haven been proposed (see Patent Literature 1).

In these fuel cells, at the time of system activation, supply ofhydrogen gas to the oxidant gas flow passage is started before thehydrogen gas spreads to at least the fuel gas flow passage, and thesupply is switched to supply of the oxidant gas to the oxidant gas flowpassage after the hydrogen gas spreads to at least the fuel gas flowpassage. Accordingly, it is considered that a corrosion reaction ofcarbon occurring in the fuel cell can be inhibited using an existing gasat the time of system activation.

CITATION LIST Patent Literature

-   [Patent Literature 1]-   Japanese Unexamined Patent Application, First Publication No.    2005-149838

SUMMARY OF INVENTION Technical Problem

In the fuel cells of the related art, oxygen in the air is supplied toan oxidant electrode. However, when oxygen is supplied instead of theair and gas leakage or the like occurs, hydrogen may drastically reactwith oxygen, and thus there is concern of causing a problem in the fuelcell due to damage or the like of a member inside the fuel cell.Accordingly, the control methods of the related art are not sufficientfrom the viewpoints of safety and reliability, and thus there is roomfor improvement.

In fuel cell systems, configurations of humidifiers or the like arenecessary to present dryness of proton conduction films. On the otherhand, simplicity, weight reduction, and space reduction of systems arefurther requested in consideration of mounting the systems on mobileobjects including investigation vehicles used on lunar surfaces or thelike.

An objective of the present invention is to provide a method ofcontrolling a fuel cell device capable of improving safety andreliability and implementing simplicity, weight reduction, and spacereduction of a system.

Solution to Problem

To achieve the foregoing objective, the present invention provides thefollowing means.

[1] There is provided a method of controlling a fuel cell device inwhich an electrolyte membrane is inserted between a fuel electrode andan oxidant electrode, hydrogen is supplied to a hydrogen supply unit ofthe fuel electrode, and a gas containing oxygen is supplied to a gassupply unit of the oxidant electrode so that power is generated. Themethod includes: a step of supplying hydrogen to the hydrogen supplyunit; a step of measuring a voltage between the fuel electrode and theoxidant electrode and determining whether the voltage is equal to orgreater than a reference voltage; and a step of discharging a gascontaining oxygen from the gas supply unit to the outside whilesupplying the gas to the gas supply unit when the voltage is equal to orgreater than the reference voltage.

[2] The method of controlling the fuel cell device according to [1] mayfurther include a step of depressurizing the hydrogen supply unit of thefuel electrode and the gas supply unit of the oxidant electrode whenpower generation of the fuel cell device is started, before the step ofsupplying the hydrogen to the hydrogen supply unit.

[3] The method of controlling the fuel cell device according to [1] mayfurther include a step of increasing current density of the fuel celldevice up to a predetermined value while performing conduction usingexternal resistance after the step of discharging the gas from the gassupply unit to the outside.

[4] In the method of controlling the fuel cell device according to [1],a circulation passage capable of connecting a gas introduction passageof the gas supply unit to a gas discharge passage may be provided. Themethod may further include: a step of determining whether impedancebetween the fuel electrode and the oxidant electrode is equal to or lessthan a predetermined threshold after the step of supplying the gascontaining oxygen to the gas supply unit; and a step of connecting thegas introduction passage of the gas supply unit and the gas dischargepassage via the circulation passage to form a circulation line andcirculating the gas of the gas discharge passage to the gas introductionpassage when the impedance is equal to or less than the predeterminedthreshold.

[5] The method of controlling the fuel cell device according to [4] mayfurther include a step of measuring a pressure difference between thehydrogen of the hydrogen supply unit and the gas of the gas supply unitand determining whether the pressure difference is greater than 0 andequal to or less than a predetermined threshold after the step ofcirculating the gas of the gas discharge passage to the gas introductionpassage. A circulation amount of the gas may be decreased when thepressured difference is greater than the predetermined threshold.

[6] In the method of controlling the fuel cell device according to [4],a circulation pump and a dehumidifier may be provided on the circulationline. The gas may be circulated while being dehumidified in thecirculation line in the step of circulating the gas of the gas dischargepassage to the gas introduction passage.

[7] In the method of controlling the fuel cell device according to [4],a circulation pump may be provided on the circulation line and in thecirculation passage. In the step of circulating the gas of the gasdischarge passage to the gas introduction passage, when the impedance isequal to or less than the predetermined threshold, the circulation pumpmay be activated in a state in which the gas is circulated from a gassupply source of the gas to the outside via the gas introductionpassage, the gas supply unit, and the gas discharge passage, andsubsequently, the gas of the gas discharge passage may be circulated tothe gas introduction passage by closing a discharge system dischargingthe gas from the gas discharge passage to the outside.

Advantageous Effects of Invention

According to the present invention, it is possible to improve the safetyand reliability and implement simplicity, weight reduction, and spacereduction of a system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically illustrating an example of aconfiguration of a fuel cell system to which a method of controlling afuel cell device according to a first embodiment of the presentinvention is applied.

FIG. 2A is a side view illustrating examples of a hydrogen supply unitand an oxygen supply unit of a separator in FIG. 1 .

FIG. 2B is a diagram illustrating a modified example of flow passagepatterns in

FIG. 2A.

FIG. 3 is a diagram illustrating a water movement model inside a fuelcell stack in FIG. 1 .

FIG. 4 is a flowchart illustrating an example of activation control ofthe fuel cell device performed in the fuel cell system in FIG. 1 .

FIG. 5 is a timing chart illustrating a change in a state of each unitwhen the activation control of the fuel cell device in FIG. 4 isperformed.

FIG. 6 is a flowchart illustrating an example of steady operationcontrol of the fuel cell device performed in the fuel cell system inFIG. 1 .

FIG. 7 is a timing chart illustrating a change in a state of each unitwhen the steady operation control of the fuel cell device in FIG. 6 isperformed.

FIG. 8 is a flowchart illustrating an example of emergency stop controlof the fuel cell device during the steady operation.

FIG. 9 is a flowchart illustrating an example of end control of the fuelcell device performed in the fuel cell system in FIG. 1 .

FIG. 10 is a timing chart illustrating a change in a state of each unitwhen activation control of the fuel cell device in FIG. 9 is performed.

FIG. 11 is a diagram schematically illustrating a configuration of afuel cell system including a hydrogen coating unit according to a secondembodiment of the present invention.

FIG. 12 is a diagram illustrating a modified example of a configurationof a fuel cell device in FIG. 11 .

FIG. 13 is a partially enlarged view illustrating a layout of a fuelcell stack in FIG. 12 .

FIG. 14 is a diagram illustrating an example of a hydrogen supply sideportion of a separator in FIG. 12 .

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

[Configuration of Fuel Cell System]

FIG. 1 is a diagram schematically illustrating an example of aconfiguration of a fuel cell system to which a method of controlling afuel cell device according to a first embodiment of the presentinvention is applied. FIG. 2A is a side view illustrating examples of ahydrogen supply unit and an oxygen supply unit (a gas supply unit) of aseparator in FIG. 1 . In the drawings used in the following description,to facilitate understanding of characteristics, characteristic portionsare enlarged for convenience in some cases, and the shapes, dimensions,ratios, and the like of constituent elements are not limited to theillustrated constituent elements.

As illustrated in FIG. 1 , a fuel cell system 1 includes a fuel celldevice 2 and a control unit 3 that generally controls the fuel celldevice 2 by transmitting and receiving signals to and from variousdevices to be described below.

In the fuel cell device 2, a fuel cell stack 21 is provided. The fuelcell stack 21 has a configuration in which a plurality of fuel cells 21Athat each include an electrolyte membrane 22, a fuel electrode 23, anoxidant electrode 24, a hydrogen supply unit 25, and an oxygen supplyunit 26 are laminated in a separator 27 (see FIG. 2A). In theembodiment, to facilitate description, a case in which the fuel cellstack 21 is configured with one fuel cell 21A will be described.

A hydrogen supply port 28 and an oxygen discharge port 29 arerespectively provided in the upper portions the fuel electrode 23 andthe oxidant electrode 24. A hydrogen discharge port 30 and an oxygensupply port 31 are respectively provided in the lower portions of thefuel electrode 23 and the oxidant electrode 24.

As illustrated in FIG. 2A, the separator 27 is formed in a flat plateshape and includes a fuel electrode side portion 32 on the front sideand an oxidant electrode side portion 33 on the rear side. In the fuelelectrode side portion 32, a hydrogen inlet 34 corresponding to thehydrogen supply port 28 and a hydrogen outlet 35 corresponding to thehydrogen discharge port 30 are provided. In the oxidant electrode sideportion 33, an oxygen inlet 36 corresponding to the oxygen supply port31 and an oxygen outlet 37 corresponding to the oxygen discharge port 29are provided. Flow passage patterns 38A and 39A of the fuel electrodeside portion 32 and the oxidant electrode side portion 33 each have, forexample, a serpentine shape and are formed so that directions (blackthick arrows in FIG. 2A) of overall flows of hydrogen flowing in thefuel electrode side portion 32 and oxygen flowing in the oxidantelectrode side portion 33 are opposite to each other. As illustrated inFIG. 2B, flow passage patterns 38B and 39B may have a pectinate shape (astraight shape). In this shape, directions (black thick arrows in FIG.2B) of overall flows of hydrogen flowing in the fuel electrode sideportion 32 and oxygen flowing in the oxidant electrode side portion 33are opposite to each other.

In the fuel cell system 1, a hydrogen supply source 41, a hydrogenintroduction passage 42 that supplies hydrogen from the hydrogen supplysource 41 to the fuel cell device 2, and a hydrogen discharge passage 43that discharges the hydrogen from the fuel cell device 2 are provided(see FIG. 1 ). The hydrogen introduction passage 42 is connected to thehydrogen supply port 28 and the hydrogen discharge passage 43 isconnected to the hydrogen discharge port 30. In the fuel cell system 1,an oxygen supply source 51, an oxygen introduction passage 52 (a gasintroduction passage) that supplies a gas (for example, oxygen) from theoxygen supply source 51 to the fuel cell device 2, and an oxygendischarge passage 53 (a gas discharge passage) that discharges the gasfrom the fuel cell device 2 are provided. The oxygen introductionpassage 52 is connected to the oxygen supply port 31 and the oxygendischarge passage 53 is connected to the oxygen discharge port 29.

In the hydrogen introduction passage 42, a three-way valve 44 isprovided. The hydrogen introduction passage 42 is connected to theoxygen introduction passage 52 via a connection flow passage 45. Thehydrogen introduction passage 42 is configured so that hydrogen can besupplied to the hydrogen supply unit 25 and hydrogen can also besupplied to the oxygen supply unit 26 via the connection flow passage45, as necessary. In the hydrogen introduction passage 42, a hydrogenpressure measurement unit 46 that measures pressure (for example, gaugepressure) of hydrogen supplied to the hydrogen supply unit 25 isprovided.

In the hydrogen discharge passage 43, a valve 47 that performsopening/blocking of a flow passage is provided and is configured so thatdischarging (purging) of hydrogen to the outside or stopping of thedischarging can be performed.

In the oxygen introduction passage 52, a valve 54 that performsopening/blocking of a flow passage is provided and is configured so thatsupplying/stopping of oxygen can be performed. In the oxygenintroduction passage 52, a gas pressure measurement unit 55 thatmeasures pressure (for example, gauge pressure) of a gas supplied to theoxygen supply unit 26 is provided.

In the oxygen discharge passage 53, a three-way valve 56 is provided.The oxygen discharge passage 53 is connected to the oxygen introductionpassage 52 via a circulation passage 57. The oxygen discharge passage 53is configured so that a gas can be discharged (purged) to the outsideand the gas can be returned to the oxygen supply unit 26 via thecirculation passage 57 as necessary. That is, in the embodiment, theoxygen introduction passage 52, the oxygen supply unit 26, the oxygendischarge passage 53, and the circulation passage 57 form a circulationline. In the circulation passage 57, a circulation pump 58, a pressureadjustment unit 59, and a flow rate measurement unit 60 are provided,and thus sending, depressurization/boosting, and flow rate measurementof a gas (for example, oxygen) are performed. The amount of gas consumedin the fuel cell system 1 can be measured by, for example, the flow ratemeasurement unit 60. The circulation amount of oxygen can be adjustedbased on a measured value of the amount of gas using the circulationpump 58. In the embodiment, the circulation pump 58 is provided in thecirculation passage 57, but the present invention is not limitedthereto. The circulation pump 58 may be provided at any position on thecirculation line, such as the oxygen discharge passage 53.

In the oxygen discharge passage 53, a condenser 61 and a dehumidifier 62are provided. The condenser 61 condenses moisture in the gas flowing inthe oxygen discharge passage 53. The dehumidifier 62 removes themoisture from the gas passing through the condenser 61 and recovers themoisture from a water recovery tank 63. The details of a configurationof the dehumidifier 62 will be described below.

In the fuel cell device 2, hydrogen (preferably, pure hydrogen) is usedas a reductant (fuel). As the oxidant, a gas containing oxygen, forexample, oxygen (preferably, pure oxygen) or air, is used. Hereinafter,the gas containing oxygen is simply referred to as a “gas.” Hydrogen issupplied to the side of the fuel electrode 23 via the hydrogen supplyport 28 and the gas is supplied to the side of the oxidant electrode 24via the oxygen supply port 31. The hydrogen and the gas supplied to theinside of the fuel cell stack 21 flow along the electrolyte membrane 22in mutually opposite directions. Water generated on the oxygen sideduring reaction of the hydrogen and the gas is moved and diffusedthrough the electrolyte membrane 22, as illustrated in FIG. 3 , and thewater is supplied to the hydrogen side. Thus, the hydrogen near thehydrogen supply port 28 is humidified. The humidified hydrogen flows ina direction opposite to the flow of the gas, the water vapor amountbecomes abundant with consumption of the hydrogen, movement of moisturefrom the hydrogen side to the oxygen side occurs near the hydrogendischarge port 30, and thus the vicinity of the oxygen supply port 31 ishumidified. As a result, inside the fuel cell stack 21, the moisturemutually moves between the gas side and the hydrogen side via theelectrolyte membrane 22.

In the fuel cell 21A, the electrolyte membrane 22 is inserted betweenthe fuel electrode 23 and the oxidant electrode 24, hydrogen is suppliedto the hydrogen supply unit 25 of the fuel electrode 23, and a gas issupplied to the oxygen supply unit 26 of the oxidant electrode 24 sothat power is generated. The fuel cell device 2 is electricallyconnected to a load 4 of a mobile object such as a vehicle to supplypower to the load 4.

The fuel cell system 1 includes the fuel cell device 2, that is, animpedance measurement unit 5 that measures impedance Z of the fuel cellstack 21, a voltage measurement unit 6 that measures a voltage V of thefuel cell stack 21, and a current measurement unit 7 that measures acurrent I flowing in the load 4. A signal in accordance with ameasurement result of the impedance measurement unit 5, a signal inaccordance with a measurement result of the voltage measurement unit 6and a signal in accordance with a measurement result of the currentmeasurement unit 7 are each transmitted to the control unit 3.

Next, activation control, steady operation control, end control of thefuel cell will be described in sequence as control of the fuel celldevice 2 applied to the fuel cell system 1.

[Activation Control]

FIG. 4 is a flowchart illustrating an example of activation control ofthe fuel cell device 2 performed in the fuel cell system 1 in FIG. 1 .FIG. 5 is a timing chart illustrating a change in a state of each unitwhen the activation control of the fuel cell device 2 in FIG. 4 isperformed. Each step of the activation control can be performed by thecontrol unit 3.

In the embodiment, as a preservation state (time t0), there is adepressurized and sealed state in which neither hydrogen nor oxygen issupplied. Accordingly, a state in which the voltage V is 0 V is apreferable state.

First, when power generation of the fuel cell device 2 starts, thehydrogen supply unit 25 of the fuel electrode 23 and the oxygen supplyunit 26 of the oxidant electrode 24 are depressurized (step S11: time t1of FIG. 5 ). For example, in the outer space, the hydrogen supply unit25 and the oxygen supply unit 26 can be depressurized by purging thehydrogen discharge passage 43 and the oxygen discharge passage 53. Underthe atmospheric pressure, the hydrogen supply unit 25 and the oxygensupply unit 26 can be depressurized by providing pumps or the like (notillustrated) in the hydrogen discharge passage 43 and the oxygendischarge passage 53. Thus, the hydrogen remaining in the hydrogensupply unit 25 is discharged and the oxygen remaining in the oxygensupply unit 26 is discharged. As will be described below, when the fuelcell device 2 is stored and each of the hydrogen supply unit 25 and theoxygen supply unit 26 is charged with a gas such as an inert gas, thegas is discharged.

Subsequently, hydrogen is supplied to the hydrogen supply unit 25 (stepS12: time t2 of FIG. 5 ). The hydrogen from the hydrogen supply source41 is supplied to the hydrogen supply unit 25 via the hydrogenintroduction passage 42. To facilitate description in FIG. 5 , pressurePH2 of the hydrogen enters the ON state at time t2, but the supplyamount may be gradually increased.

Thereafter, a voltage between the fuel electrode 23 and the oxidantelectrode 24 is measured and it is determined whether the voltage isequal to or greater than a reference voltage Vs1 (step S13). The valueof the reference voltage Vs1 (an electromotive force) is notparticularly limited and is, for example, 100 mV. In this step, it canbe checked whether hydrogen is normally supplied to the hydrogen supplyunit 25 by using a difference in the potential between both theelectrodes generated to correspond to hydrogen density, that is, anelectromotive force of a concentration cell.

When the voltage between the fuel electrode 23 and the oxidant electrode24 is equal to or greater than the reference voltage Vs1 (YES in stepS13), it is determined that the hydrogen is normally supplied to thehydrogen supply unit 25 and the gas is discharged from the oxygen supplyunit 26 to the outside while supplying a gas to the oxygen supply unit26 (step S14: time t3 of FIG. 5 ). At this time, the circulation pump 58may be operated to circulate the gas via the circulation passage 57.When the gas is oxygen, the supply amount of oxygen is not particularlylimited and is, for example, 0.5 to 10 times the supply amount ofhydrogen. When oxygen is supplied as an oxidant, flooding easily occurs.Therefore, a supply amount of oxygen is increased more than in a case inwhich air is used as the oxidant. In this step, desorption of themoisture from the electrolyte membrane 22 is accelerated by the flow ofthe oxygen in the oxygen supply unit 26, unnecessary moisture isdischarged to the outside along with the oxygen, and thus the occurrenceof the flooding can be presented.

When the voltage between the fuel electrode 23 and the oxidant electrode24 is less than the reference voltage Vs1 (NO in step 13), the processreturns to step S12 to continue the supply of the hydrogen to thehydrogen supply unit 25. When the voltage is less than the referencevoltage Vs1 despite the continuous supply of the hydrogen to thehydrogen supply unit 25 for a predetermined time or more which has beenpre-decided, it is determined that a failure occurs in the fuel cellsystem 1. Then, the activation control is stopped.

When oxygen is supplied as an oxidant, leakage of the hydrogen occursdue to some reason, and the oxygen is supplied to the oxygen supply unit26, the hydrogen with reacts with the oxygen radically. Thus, due to thereaction, there is concern of the fuel cell stack 21 being broken down.Further, when a gas is supplied to the oxygen supply unit 26 before thesupply of the hydrogen to the hydrogen supply unit 25, carbon of acatalytic layer of an electrode adjacent to, particularly, theelectrolyte membrane 22 is oxidized. Thus, the oxidation of the carboncauses occurrence of breakdown or deterioration of the fuel cell stack21. By supplying the hydrogen to the hydrogen supply unit 25 andsupplying the gas to the oxygen supply unit 26 as in this step, it ispossible to prevent occurrence of radical reaction of the hydrogen andthe oxygen and prevent deterioration or breakdown of the fuel cell stack21.

Subsequently, current density (or the current I) of the fuel cell device2 is increased up to a predetermined value Is while performingconduction using external resistance (step S15: times t4 to t5 of FIG. 5). The predetermined value Is of the current density is not particularlylimited and is, for example, 0 to 0.1 A/cm². As described above, forexample, the load 4 such as a heater or a motor used in a closedenvironment is connected to the fuel cell device 2. By decreasing theload 4 (resistance), it is possible to increase the current density ofthe fuel cell device 2.

Thereafter, it is determined whether impedance Z between the fuelelectrode 23 and the oxidant electrode 24 is equal to or less than apredetermined threshold Zs (step S16: time t5 of FIG. 5 ). Thepredetermined threshold of the impedance Z is not particularly limitedand is, for example, 5 mΩ to 20 mΩ at 1 kHz. When the moisture in theelectrolyte membrane 22 is insufficient, the impedance Z is increased.Thus, when the impedance Z is equal to or less than the predeterminedthreshold, it can be determined that the amount of moisture in theelectrolyte membrane 22 is appropriate, and thus it is possible toinhibit occurrence of dry-out. In particular, when air is used as anoxidant, dry-out easily occurs. Therefore, in this step, it can bechecked with high accuracy whether dry-out occurs.

When the impedance Z between the fuel electrode 23 and the oxidantelectrode 24 is equal to or less than the predetermined value Zs (YES instep S16), the valve 47 is closed to block a flow passage to thehydrogen discharge passage 43. Thereafter, the oxygen introductionpassage 52 and the oxygen discharge passage 53 of the oxygen supply unit26 are connected via the circulation passage 57 to form the circulationline. Then, the gas of the oxygen discharge passage 53 returns to theoxygen introduction passage 52 (step S17: time t6 of FIG. 5 ). In thisway, the differential pressure between the fuel electrode 23 and theoxidant electrode 24 is appropriately maintained.

When the impedance Z between the fuel electrode 23 and the oxidantelectrode 24 exceeds the predetermined value Zs (NO in step S16), it isdetermined that dry-out occurs and a circulation amount of oxygen isdecreased. When the voltage is less than a predetermined value lowerthan the reference voltage Vs1 despite the impedance Z which is equal toor less than the threshold Zs, it can be determined that flooding occursand the circulation amount of oxygen can be increased.

When the circulation pump 58 and the dehumidifier 62 are provided on thecirculation line, the gas may be circulated in the foregoing step S17while dehumidifying the gas using the dehumidifier 62 provided on thecirculation line. Thus, it is possible to remove unnecessary moisturefrom the gas flowing in the circulation line and it is possible tofurther inhibit the occurrence of the flooding. In particular, whenoxygen is used as an oxidant, flooding easily occurs. Therefore, in thisstep, it is possible to reliably inhibit occurrence of flooding.

When the circulation pump 58 is provided in the circulation passage 57on the circulation line (see FIG. 1 ) and the impedance Z is equal to orless than the predetermined threshold Zs in the foregoing step S17, thecirculation pump 58 can be activated in a state in which the gas iscirculated from the hydrogen supply source 51 of the gas to the outsidevia the oxygen introduction passage 52, the oxygen supply unit 26, andthe oxygen discharge passage 53. In this case, the gas of the oxygendischarge passage 53 returns to the oxygen introduction passage 52 byclosing a discharge system discharging the gas from the oxygen dischargepassage 53 to the outside. The closing of the discharge system can beperformed using, for example, the three-way valve 56. Thus, the wholegas flowing in the oxygen discharge passage 53 is sent to the oxygenintroduction passage 52 via the circulation passage 57, and thus is in astate in which the gas is not discharged to the outside.

Subsequently, a pressure difference ΔP between the hydrogen of thehydrogen supply unit 25 and the gas of the oxygen supply unit 26 ismeasured and it is determined whether the pressure difference ΔP isequal to or less than a predetermined threshold (step S18). Thepredetermined threshold is not particularly limited and is, for example,greater than 0 and is 50 kPa (0<ΔP<50 kPa). When the pressure differenceΔP is greater than the predetermined threshold (YES in step S18), thecirculation amount of gas is decreased (step S19). By setting thepressure difference to be equal to or less than the predeterminedthreshold, it is possible to prevent breaking of the electrolytemembrane 22 due to a gas pressure. It is preferable to set a pressurePGAS of the gas to be higher than a pressure PH2 of the hydrogen(ΔP=PGAS−PH2). Thus, it is possible to implement safer operation. Whenthe pressure difference ΔP is equal to or less than the predeterminedthreshold (NO in step S18), the activation control ends and the processproceeds to steady operation control to be described below.

As described above, according to the activation control, the hydrogen issupplied to the hydrogen supply unit 25 (step S12). When the voltage Vbetween the fuel electrode 23 and the oxidant electrode 24 is equal toor greater than the reference voltage Vs1 (YES in step S13), the gas isdischarged from the oxygen supply unit 26 to the outside while supplyingthe gas to the oxygen supply unit 26 (step S14). Therefore, it can bedetermined accurately whether the hydrogen is normally supplied to thehydrogen supply unit 25 by using the reference voltage and the gas issupplied to the oxygen supply unit 26 based on a determination result.Therefore, it is possible to prevent occurrence of deterioration orbreakdown of the fuel cell stack 21. Accordingly, it is possible toprevent occurrence of a problem in the fuel cell device 2 during theactivation and it is possible to improve safety and reliability.

[Steady Operation Control]

FIG. 6 is a flowchart illustrating an example of steady operationcontrol of the fuel cell device 2 performed in the fuel cell system 1 inFIG. 1 . FIG. 7 is a timing chart illustrating a change in a state ofeach unit when the steady operation control of the fuel cell device 2 inFIG. 6 is performed. Each step of the steady operation control can beperformed by the control unit 3 similarly to the foregoing activationcontrol.

First, during a steady operation of the fuel cell device 2, it isdetermined whether the impedance Z between the fuel electrode 23 and theoxidant electrode 24 is greater than the predetermined threshold (stepS21). The predetermined threshold of the impedance Z may be measured as,for example, 1 kHz (a fixed value), as described above, and may be setbased on about three points of the impedance appropriate between 10 mHzto 1 kHz. When the predetermined threshold is set based on about threepoints of the impedance, impedance data (a Nyquist diagram) can beacquired, three points of frequency indicating typical impedance can bedetermined, and the predetermined threshold can be determined using theimpedance at that time, for example, in a state in which the fuel celldevice 2 is sound.

When the impedance Z is greater than the predetermined threshold (YES instep S21: time t31 of FIG. 7 ), dry-out in the electrolyte membrane 22is determined and a flow rate of the gas circulating via the circulationpassage 57 connecting the oxygen introduction passage 52 to the oxygendischarge passage 53 is decreased (step S22: time t31 to t32 of FIG. 7). Thus, the discharge of the moisture in the electrolyte membrane 22can be inhibited by the flow of the gas of the oxygen supply unit 26 andthe electrolyte membrane 22 can enter an appropriate humidified state.

In step S22, the occurrence of dry-out is determined based on theimpedance Z, but the present invention is not limited thereto. Theoccurrence of the dry-out may be determined based on one or a pluralityof current interruption, a load change, and DC resistance. Theoccurrence of the dry-out may be determined based on the impedance Z andone or a plurality of, current interruption, a load change, and DCresistance. Thus, it is possible to determine the occurrence of thedry-out more accurately.

In the embodiment, when the impedance Z is greater than thepredetermined threshold, the flow rate of the gas circulating via thecirculation passage 57 is decreased, but the present invention is notlimited thereto. A flow rate of the gas circulating via the circulationpassage 57 may be decreased and a flow rate of the gas may be decreased.Thus, the electrolyte membrane 22 can enter an appropriate humidifiedstate in a shorter amount of time.

Conversely, when the impedance Z is equal to or less than thepredetermined threshold (NO in step S21), the voltage V between the fuelelectrode 23 and the oxidant electrode 24 is measured and it isdetermined whether the voltage V is equal to or less than the firstpredetermined threshold (step S23). The first predetermined threshold ofthe voltage V is not particularly limited and is, for example, a valuein the range of 500 mV to 600 mV.

When the voltage V is equal to or less than the first predeterminedthreshold (YES in step S23): time t33 to t34 of FIG. 7 ), flooding isdetermined and a flow rate of the gas circulating via the circulationpassage 57 is increased (step S24: time t33 to t34 of FIG. 7 ). Forexample, when the impedance Z is equal to or less than the predeterminedthreshold and the voltage V is equal to or less than the firstpredetermined threshold, an ejection amount of the circulation pump 58is increased and the circulation amount of gas is increased. Thus, thedischarge of the moisture in the electrolyte membrane 22 by the flow ofthe gas of the oxygen supply unit 26 can be accelerated and theelectrolyte membrane 22 can enter an appropriate humidified state. Whenthe voltage V exceeds the first predetermined threshold in the controlof step S24, the flow rate of the gas circulating via the circulationpassage 57 is returned to the steady state (time t35 of FIG. 7 ).

When the voltage V is equal to or less than the first predeterminedthreshold in step S24, a flow rate of the gas circulating via thecirculation passage 57 is increased, but the present invention is notlimited thereto. The flow rate of the gas circulating via thecirculation passage 57 may be increased and the flow rate of the gas maybe increased. Thus, the electrolyte membrane 22 can enter an appropriatehumidified state in a shorter amount of time.

Subsequently, it is determined again whether the voltage V between thefuel electrode 23 and the oxidant electrode 24 is equal to or less thanthe first predetermined threshold (step S25). When the voltage V isequal to or less than the first predetermined threshold in theredetermination (YES in step S25), the hydrogen supply unit 25 is purged(step S26: time t34 of FIG. 7 ) and a subsequent operation is stopped(step S27). In general, the electrolyte membrane 22 can enter anappropriate humidified state by performing the foregoing adjustment ofthe flow rate of the gas. However, the voltage V is not recovered to anormal value due to some reason in some cases. In these cases, bypurging the hydrogen supply unit 25 in step S27, the moisture in theelectrolyte membrane 22 can be discharged through the purging and thevoltage V can be recovered to a normal value equal to or greater thanthe first predetermined threshold.

When the voltage V is greater than the first predetermined threshold instep S23 (NO in step S23) or the voltage V is greater than the firstpredetermined threshold in the redetermination of step S25 (NO in stepS25), the process returns to step S21. The process proceeds to endcontrol to be described below, as necessary.

A method of purging the hydrogen supply unit 25 is not particularlylimited. For example, in the outer space, a capillary (not illustrated)is provided in the hydrogen discharge passage 43 and hydrogen isreleased to the outer space via the capillary. Since the fuel celldevice 2 is normally disposed in pressurized cabin where people act, thehydrogen of the hydrogen discharge passage 43 is gradually depressurizedand sudden discharge of the hydrogen is prevented. Thus, it is possibleto purge the hydrogen supply unit 25 safely in a simple configuration.

When the voltage V is equal to or less than the first predeterminedthreshold, the hydrogen supply unit 25 is purged in step S27, but thepresent invention is not limited thereto. When the voltage V is equal toor less than the first predetermined threshold, the hydrogen supply unit25 may be purged and the hydrogen supply unit 25 may be purgedperiodically at a separate predetermined timing. The predeterminedtiming of the purging is not particularly limited and is, for example,an interval of 15 minutes.

Further, a warm retaining member (not illustrated) may be provided inthe hydrogen introduction passage 42 or the hydrogen discharge passage43. Thus, condensation or freezing which can occur due to the purging ofthe hydrogen supply unit 25 can be prevented and safer and more reliablepurging can be performed.

As described above, according to the steady operation control, when theimpedance Z between the fuel electrode 23 and the oxidant electrode 24is greater than the predetermined threshold (YES in step S21), the flowrate of the gas circulating via the circulation passage 57 is decreased(step S22). Conversely, when the impedance Z is equal to or less thanthe predetermined threshold (NO in step S21), it is determined whetherthe voltage V between the fuel electrode 23 and the oxidant electrode 24is equal to or less than the first predetermined threshold (step S23).When the voltage V is equal to or less than the first predeterminedthreshold, the flow rate of the gas circulating in the circulationpassage 57 is increased. That is, by using both the impedance Z and thevoltage V, it can be accurately determined whether any of dry-out andflooding occurs during power generation of the fuel cell device 2 andthe electrolyte membrane 22 can enter an appropriate humidified statebased on the determination result. Accordingly, it is possible toprevent both occurrence of flooding and occurrence of dry-out and it ispossible to implement power generation in which good water balance ismaintained.

(Emergency Stop Control)

FIG. 8 is a flowchart illustrating an example of emergency stop controlof the fuel cell device 2 during the steady operation. The emergencystop control is performed independently or in parallel with theforegoing steady operation control. Each step of an emergency stopmethod can be performed by the control unit 3 similarly to the steadyoperation control.

The emergency stop control is performed when a temperature Tf of thefuel cell stack 21 of the fuel cell device 2 is greater than apredetermined threshold (YES in step S31), oxygen is detected in thehydrogen supply unit 25 (YES in step S32), or the voltage V between thefuel electrode 23 and the oxidant electrode 24 is less than a secondpredetermined threshold (YES in step S33) and therefore an occurrence ofabnormality of the fuel cell device 2 is determined.

The predetermined threshold of the temperature Tf is not particularlylimited and is, for example, 90 to 100° C. Thus, temperature abnormalityof the fuel cell device 2 can be detected and the fuel cell device 2 canbe stopped safely. Oxygen in the hydrogen supply unit 25 can be detectedby, for example, providing, an oxygen sensor (not illustrated) in thehydrogen supply unit 25. Thus, leakage of the oxygen in the fuel celldevice 2 can be detected and the fuel cell device 2 can be stoppedsafely. The second predetermined threshold of the voltage V is notparticularly limited and is a value less than the first predeterminedthreshold of the voltage V. For example, when power is generated withhydrogen/oxygen, the second predetermined threshold is 400 mV to 500 mVper cell. Thus, when much water is generated by the fuel cell device 2,the fuel cell device 2 can be stopped safely.

Determining occurrences of abnormalities may be determined in successionin FIG. 7 or may be performed in parallel at an appropriate timing

When the temperature Tf of the fuel cell stack 21 is greater than thepredetermined threshold, oxygen is detected in the hydrogen supply unit25, or the voltage V is less than the second predetermined threshold,the load 4 connected to the fuel cell stack 21 is first decreased (stepS34). For example, the load 4 (resistance) is decreased based on anabnormality signal transmitted from the control unit 3.

Subsequently, the supply of the gas to the oxygen supply unit 26 isstopped and the circulation of the gas circulating in the circulationpassage 57 connecting the oxygen introduction passage 52 to the oxygendischarge passage 53 is stopped (step S35). For example, the valve 54provided upstream from the oxygen introduction passage 52 is closed tostop the supply of the gas to the oxygen supply unit 26. In thethree-way valve 56 provided in the oxygen discharge passage 53, thesupply of the gas from the oxygen discharge passage 53 to thecirculation passage 57 is stopped and the gas is discharged from theoxygen discharge passage 53 to the outside. Besides, the circulationpump 58 of the circulation passage 57 may be stopped.

Further, the hydrogen supply unit 25 and the oxygen supply unit 26 aredepressurized (step S36). A method of depressurizing the hydrogen supplyunit 25 is not particularly limited. In the outer space, for example,the hydrogen discharge passage 43 is opened to the outer space todischarge the hydrogen to the outer space, similarly to the purgingmethod. A method of depressurizing the oxygen supply unit 26 can also beperformed by opening the oxygen discharge passage 53 to the outer spaceand discharging the gas to the outer space, similarly to the method ofdepressurizing the hydrogen supply unit 25. Thus, the hydrogen can becaused to not remain in the hydrogen supply unit 25 and the gas can alsobe caused to not remain in the oxygen supply unit 26.

According to the emergency stop method, the fuel cell device 2 can bestopped safely when an environment in which an emergency is requiredduring a steady operation of the fuel cell device 2 occurs.

When at least two of the three types of abnormality described above aresatisfied, the load 4 connected to the fuel cell stack 21 may bedecreased, the supply of the gas to the oxygen supply unit 26 may bestopped, the circulation of the gas via the circulation passage 57 maybe stopped, and the hydrogen supply unit 25 and the oxygen supply unit26 may be further depressurized. Thus, it is possible to set conditionsfor the emergency stop more strictly and it is possible to preventemergency stop caused due to erroneous detection.

[End Control]

FIG. 9 is a flowchart illustrating an example of end control of the fuelcell device 2 performed in the fuel cell system 1 in FIG. 1 . FIG. 10 isa timing chart illustrating a change in a state of each unit when theend control of the fuel cell device 2 in FIG. 8 is performed. Each stepof the end control can be performed by the control unit 3, similarly toan activation operation.

When an operation of the fuel cell device 2 in which the steadyoperation control is performed (time t30 to t31 of FIG. 7 ) ends, theload 4 is first decreased (step S41: time t21 to t22 of FIG. 10 ).Thereafter, the hydrogen discharge passage 43 is opened, the hydrogensupply unit 25 of the fuel electrode 23 is purged, the oxygen dischargepassage 53 is opened, and the oxygen supply unit 26 of the oxidantelectrode 24 is purged (step S42: time t22 of FIG. 10 ). A method ofpurging the hydrogen supply unit 25 and a method of purging the oxygensupply unit 26 can be performed, for example, similarly to the foregoingpurging method. Thus, the hydrogen inside the hydrogen supply unit 25 isdischarged to the outside and the gas inside the oxygen supply unit 26is discharged to the outside.

After the purging of step S42 is cancelled (time t23 of FIG. 10 ), thevoltage V between the fuel electrode 23 and the oxidant electrode 24 ismeasured and it is determined whether the voltage V is greater than apredetermined threshold Vs2 (step S43). The predetermined threshold Vs2of the voltage V is not particularly limited as long as thepredetermined threshold Vs2 is a voltage at which a catalyzer of anelectrode is oxidized. For example, the predetermined threshold Vs2 is300 mV per cell. When the voltage V is greater than the predeterminedthreshold Vs2 (YES in step S43), power generation in the fuel celldevice 2 continues until the voltage V becomes equal to or less than thepredetermined threshold Vs2 (step S44: time t23 to t24 of FIG. 10 ).Since both the hydrogen supply unit 25 of the fuel electrode 23 and theoxygen supply unit 26 of the oxidant electrode 24 are purged, thevoltage V between the fuel electrode 23 and the oxidant electrode 24 canbe decreased due to the power generation of this step.

When the voltage V is equal to or less than the predetermined thresholdVs2 (NO in step S43), the hydrogen supply unit 25 and the oxygen supplyunit 26 are depressurized (step S45: time t24 of FIG. 10 ). A method ofdepressurizing the hydrogen supply unit 25 and a method ofdepressurizing the oxygen supply unit 26 can also be performed,similarly to the depressurizing method. Thus, the hydrogen can be causedto not remain in the hydrogen supply unit 25 and the gas can also becaused to not remain in the oxygen supply unit 26.

Thereafter, the fuel electrode 23 and the oxidant electrode 24 areshort-circuited as necessary (step S46: time t25 of FIG. 10 ) and theprocess ends. Thus, a potential difference between the fuel electrode 23and the oxidant electrode 24 can be set to 0 reliably. Theshort-circuiting between the fuel electrode 23 and the oxidant electrode24 can be performed, for example, by electrically connecting a switch(not illustrated) to the fuel cell device 2 in parallel.

When the voltage V is equal to or less than the predetermined thresholdVs2 (NO in step S43), the hydrogen supply unit 25 and the oxygen supplyunit 26 may be filled with hydrogen or an inert gas. When the oxygensupply unit 26 is filled with hydrogen, the hydrogen can be sent fromthe hydrogen introduction passage 42 via the connection flow passage 45to the oxygen introduction passage 52. Thus, a catalyst of an electrodeof the fuel cell device 2, particularly, the oxidant electrode 24, canbe maintained in a further unoxidized state. Since the hydrogen supplyunit 25 and the oxygen supply unit 26 are filled with hydrogen with thevoltage V being sufficiently low, deterioration of the catalyst causeddue to an oxidation reaction including combustion can be avoided.

The hydrogen with which the hydrogen supply unit 25 and the oxygensupply unit 26 are filled can be discharged to the outside through thedepressurization performed in step S11 (see FIG. 4 ) of the activationcontrol during subsequent activation.

The hydrogen supply unit 25 and the oxygen supply unit 26 may be filledwith hydrogen or the like when the voltage V is equal to or less thanthe predetermined threshold Vs2 and before the hydrogen supply unit 25and the oxygen supply unit 26 are depressurized. The hydrogen supplyunit 25 and the oxygen supply unit 26 may be filled with hydrogen or thelike when the voltage V is equal to or less than the predeterminedthreshold Vs2 and after the hydrogen supply unit 25 and the oxygensupply unit 26 are depressurized.

The fuel electrode 23 and the oxidant electrode 24 may beshort-circuited after the hydrogen supply unit 25 and the oxygen supplyunit 26 are filled with hydrogen or an inert gas. Thus, deterioration ofthe catalyst caused due to combustion can be avoided reliably.

As described above, according to the end control, the hydrogen supplyunit 25 of the fuel electrode 23 is purged and the oxygen supply unit 26of the oxidant electrode 24 is purged (step S42). When the voltage Vbetween the fuel electrode 23 and the oxidant electrode 24 is greaterthan the predetermined threshold Vs2, the power generation in the fuelcell device 2 continues (step S44). When the voltage V is equal to orless than the predetermined threshold Vs2, the hydrogen supply unit 25and the oxygen supply unit 26 are depressurized (step S45). Therefore,in a state in which the hydrogen rarely remains in the hydrogen supplyunit 25 and the gas rarely remains in the oxygen supply unit 26, theoperation of the fuel cell device 2 can be ended, the fuel cell device 2can be stored in a safe state until subsequent activation, and the fuelcell device 2 can also be activated safely during the subsequentactivation.

[Another Configuration of Fuel Cell System]

FIG. 11 is a diagram schematically illustrating a configuration of afuel cell system including a hydrogen coating unit according to a secondembodiment of the present invention. The configuration of the fuel cellsystem in FIG. 11 is basically the same as the configuration of the fuelcell system 1 in FIG. 1 , and other portions will be described below.

As illustrated in FIG. 11 , the fuel cell device 2 according to theembodiment includes the fuel cell stack 21, a hydrogen coating unit 71that is disposed to cover the fuel cell stack 21 and is configured sothat the inside is filled with hydrogen, and a hydrogen introductionunit 72 in which hydrogen is introduced to the hydrogen coating unit 71.

The hydrogen coating unit 71 is a container that accommodates the fuelcell device 2 in an inner space and is able to seal the inner space. Thehydrogen coating unit 71 has any of various shapes such as a rectangularparallelopiped shape or a cylindrical shape. A bag shape or a barrelshape is preferable from the viewpoint of strength. The hydrogen coatingunit 71 is preferably formed of a material with which neutrons can beshielded and is formed of, for example, metal such as aluminum. Theinside of the hydrogen coating unit 71 is preferably maintained in astate in which pressurization is achieved by hydrogen. Thus, even whenminute crack or the like occurs in the hydrogen coating unit 71, ahydrogen-filled state can be maintained.

The hydrogen introduction unit 72 is connected to, for example, anothersystem and supplies hydrogen from a hydrogen supply source provided inthe other system to the hydrogen coating unit 71. The hydrogenintroduction unit 72 may be connected to a hydrogen tank 41A serving asa hydrogen supply source. In this case, hydrogen from the hydrogen tank41A can be supplied to one or both of the hydrogen supply unit 25 andthe hydrogen coating unit 71. In the embodiment, an oxygen tank 51Bserving as a gas supply source is provided, and oxygen of the oxygentank 51B is supplied to the oxygen introduction passage 52.

The fuel cell device 2 includes a capillary port (port) 73 thatcommunicates with the fuel cell stack 21 and discharges water generatedinside the fuel cell stack 21 to the outside of the hydrogen coatingunit 71 and a purge port 74 that is provided in the hydrogen coatingunit 71 and is able to open the inner space of the hydrogen coating unit71. The capillary port 73 is opened to, for example, the outer space.When flushing occurs or a tendency of the flooding emerges, anunnecessary gas or moisture inside the hydrogen coating unit 71 isdischarged to the outer space by opening a valve provided in thecapillary port 73. In the capillary port 73, at least a downstream tipend portion 73 a preferably has a capillary shape. Thus, sudden purgecan be inhibited and a gas can be gradually discharged to the outerspace. The purge port 74 is opened to, for example, the outer space. Ina case in which safety guarantee is necessary or in emergency, the gasor the like inside the hydrogen coating unit 71 can be purged as quicklyas possible by opening or breaking a valve provided in the purge port74.

FIG. 12 is a diagram illustrating a modified example of a configurationof the fuel cell device 2 in FIG. 11 .

As illustrated in FIG. 12 , the fuel cell device 2 according to amodified example includes the hydrogen coating unit 71, the hydrogenintroduction unit 72, and a hydrogen discharge unit 75 that dischargeshydrogen from the hydrogen coating unit 71. An inner space A of thehydrogen coating unit 71 communicates with the hydrogen supply unit 25(see FIG. 11 ). Hydrogen is supplied to the hydrogen supply unit 25 byintroducing the hydrogen from the hydrogen introduction unit 72 to thehydrogen coating unit 71. That is, in the fuel cell device 2 in FIG. 12, one hydrogen gas system is formed by the hydrogen introduction unit72, the inner space A of the hydrogen coating unit 71, and the hydrogendischarge unit 75. The hydrogen gas system supplies hydrogen to thehydrogen coating unit 71 and supplies hydrogen to the hydrogen supplyunit 25.

In the modified example, as illustrated in FIG. 13 , the fuel electrode23, the electrolyte membrane 22, and the oxidant electrode 24 arelaminated in this order in the vertical direction (for example, adirection D3 in the drawing). In this case, the fuel electrode 23 ispreferably disposed below the electrolyte membrane 22. In this way, thefuel cell stack 21 is horizontally (transversely) disposed. Thus, undera gravitational environment, both the hydrogen flowing in the hydrogensupply unit 25 and the gas flowing in the oxygen supply unit 26 can flowin a direction perpendicular to the vertical direction. Thus, a good gasflow in which the influence of gravity is small can be implemented.

In the separator 27 (see FIGS. 2A and 2B), a hydrogen supply sideportion 76 has a plurality of grooves 76 a formed throughout in alongitudinal direction (a direction D1 in FIG. 12 ) of the fuel cellstack 21, for example, as illustrated in FIG. 14 . The upper portions ofthe plurality of grooves 76 a are blocked by lamination of the fuelcell. Thus, a plurality of flow passage patterns communicating with theinner space A of the hydrogen coating unit 71 are formed.

Here, in an environment in which electron ray density is high like alunar surface, there is concern of deterioration or the like in theelectrolyte membrane due to radioactive rays transmitting through thefuel cell stack 21. In the fuel cell device 2 according to the modifiedexample, neurons are shielded by the hydrogen with which the hydrogencoating unit 71 is filled. In the configuration in which the hydrogencoating unit 71 is filled with hydrogen, as illustrated in FIG. 13 ,even in a structure in which the hydrogen supply side portion 76 of theseparator 27 has a simple flow passage pattern such as a groove shape,hydrogen serving as a base of the foregoing reference voltage can becontinuously supplied to the separator 27 while using the separator 27that has the configuration. By using one hydrogen gas system, it ispossible to supply hydrogen to the hydrogen supply unit 25 while fillingthe hydrogen coating unit 71 with hydrogen. Thus, the fuel cell devicecan be simplified.

The fuel cell device 2 may include a neutron shielding member 77provided between the hydrogen coating unit 71 and the fuel cell stack 21(see FIG. 12 ). A position at which the neutron shielding member 77 isdisposed is not particularly limited. For example, the neutron shieldingmember 77 is disposed on an inner surface of the hydrogen coating unit71 and is preferably disposed to cover the fuel cell stack 21. The shapeof the neutron shielding member 77 is not particularly limited and anyof various shapes such as a sheet shape can be used. The neutronshielding member 77 is formed of, for example, beryllium, an alloy withberyllium, or a material containing a heavy metal. For example, lead oran alloy with lead is an exemplary example of the heavy metal.

The fuel cell device 2 may include a moisture absorption member 78mounted on the fuel cell stack 21. In this case, an upstream end portion73 b of the capillary port 73 comes into contact with the moistureabsorption member 78 or is disposed near the moisture absorption member78. The moisture absorption member 78 is formed as, for example, a meshmember or a porous member. For example, a wick is an exemplary exampleof the mesh member. Thus, since water generated inside the hydrogencoating unit 71 is discharged to the outer space via the moistureabsorption member 78, the discharge amount of hydrogen at the time ofdischarge of water from the capillary port 73 can be reduced.

The moisture absorption member 78 may be disposed on the lower surfaceof the fuel cell stack 21. Under a gravitational environment, themoisture absorption member 78 can be spread all over below the fuel cellstack 21, and thus can function as a buffer at the time of discharge ofwater necessary in an emergency.

A portion including the position at which the moisture absorption member78 is disposed may be cooled so that a temperature is relatively lowerthan in the other portions of the hydrogen coating unit 71. Thus, wateris easily generated in the moisture absorption member 78, and thus it ispossible to further reduce the discharge amount of hydrogen when wateris discharged from the capillary port 73.

In the fuel cell system 1 according to the embodiment, the dehumidifier62 is connected to the oxygen discharge passage 53 of the oxygen supplyunit 26 and is able to be switched from one water recovery tank 63 toanother water recovery tank 63 (see FIG. 11 ). The control unit 3switches the water recovery tank 63 based on a product (t)×(I) of acurrent value (I) and a conduction time (t) to the load 4 connected tothe fuel cell stack 21.

Under a closed environment and an oxygen supply environment, much wateris generated in a short time although efficient recovery of water isrequired. With detection of an amount of water in the water recoverytank 63, water may overflow inside the fuel cell system 1 when breakdownor the like of a sensor for determining the amount of water occurs, andthere is a possibility of a problem such as power generation stop andfurther flooding occurring. In the embodiment, by using the dehumidifier62 equipped to be able to be switched between the plurality of waterrecovery tanks 63, the control unit 3 measures the conduction time (t)to the load 4 and the current measurement unit 7 measures the currentvalue (I) to calculate the product (t)×(I). When the calculated value ofthe product (t)×(I) is equal to or greater than a predeterminedthreshold set based on correlation between the product (t)×(I) and thetheoretical generation amount of water, it is determined that the waterrecovery tank 63 which is being used is full of water up to a capacityand one water recovery tank 63 which is being used is switched toanother unused water recovery tank 63. Thus, it is possible to reliablyprevent leakage of water inside the fuel cell system 1 and furtherprevent occurrence of a problem such as flooding.

The fuel cell system 1 may include a temperature measurement unit 81that measures a temperature of the fuel cell stack 21 (or the fuel cell21A) and a temperature adjustment unit 82 that performs temperatureregulation of the fuel cell stack 21. In this case, the control unit 3transmits a control signal to the temperature adjustment unit 82 basedon a measured value of a temperature of the fuel cell stack 21. Thetemperature adjustment unit 82 cools or heats the fuel cell stack 21based on the control signal transmitted from the control unit 3. Thus,it is possible to maintain the fuel cell stack 21 at an appropriatetemperature during power generation.

The temperature measurement unit 81 may include, for example, ahydrogen-side temperature sensor mounted on a hydrogen line of the fuelcell stack 21 and a gas-side temperature sensor mounted on a gas(oxygen) line.

The temperature regulation of the fuel cell stack 21 is not particularlylimited and is, for example, of a water-cooling type. In the temperatureregulation of the water-cooling type, water generated through powergeneration of the fuel cell device 2 can be used.

The control unit 3 or the temperature adjustment unit 82 may perform thetemperature regulation of the fuel cell stack 21 based on a measuredvalue of the voltage V of the fuel cell stack 21 transmitted from thevoltage measurement unit 6. The control unit 3 or the temperatureadjustment unit 82 may record the measured value of the voltage V of thefuel cell stack 21 to be readable on a recording medium such as a datalogger.

The fuel cell system 1 may include a battery 8 electrically connected tothe fuel cell stack 21 in parallel (see FIG. 11 ). The battery 8 isconnected to a power system inside a mobile object and can supply powerto another power system, for example, when sufficient power generationis difficult in the fuel cell device 2, such as the time of abnormalitydetection or the time of activation. When the battery 8 is used only atthe time of activation, the battery 8 can be set to have a minimumnecessary capacity. Thus, the battery 8 can be miniaturized and spacereduction can be achieved.

By connecting the battery 8 to the fuel cell stack 21 in this way, it ispossible to return a mobile object in an emergency using the battery 8as an emergency power when any problem occurs in the fuel cell device 2.The battery 8 may be connected to a solar photovoltaic device or atemperature difference power generation device mounted on a rover. Inthis case, in lunar surface investigation, the battery 8 can besupplementarily charged with power generated with the solar photovoltaicdevice or the temperature difference power generation device.

As described above, according to the embodiment, the hydrogen coatingunit 71 is disposed to cover the fuel cell stack 21 and is configured tobe filled with hydrogen therein. The hydrogen introduction unit 72introduces hydrogen to the hydrogen coating unit 71. Therefore, bycoating the fuel cell stack 21 with hydrogen, it is possible to inhibitenergy loss of neutrons due to collision with hydrogen and considerablyinhibit deterioration and wearing of the electrolyte membrane 22. Thus,it is possible to prevent occurrent of deterioration or breakdown of thefuel cell stack 21. Since hydrogen used as a reductant of the fuel cellstack 21 is also used as a filler material in the inner space of thehydrogen coating unit 71, it is not necessary to provide a neutronshielding member separately. It is possible to implement simplicity,weight reduction, and space reduction of the system.

The embodiments of the present invention have been described in detailabove, but the present invention is not limited to the foregoingembodiments. Various modifications can be made within the scope of thegist of the present invention described in the claims.

For example, a method of controlling the fuel cell system and the fuelcell device can also be applied as a method for the outer space to avehicle such as rover used for lunar investigation. The method can beapplied as a method for the ground to a mobile object such as a vehicleused under a gravitational environment, such as a fuel cell vehicle.

By combining the oxidation reaction of hydrogen performed in the fuelcell device and the decomposition reaction of water, it is possible torepeat the power generation reversibly and it is possible to construct aconsiderably useful regenerative fuel cell system. In particular, theforegoing system can be applied as a system for the ground toregenerative energy storage and transportation hydrogen production.

INDUSTRIAL APPLICABILITY

According to the method of controlling the fuel cell, it is possible toimprove the safety and reliability and implement simplicity, weightreduction, and space reduction of a system.

REFERENCE SIGNS LIST

-   -   1 Fuel cell system    -   2 Fuel cell device    -   3 Control unit    -   4 Load    -   5 Impedance measurement unit    -   6 Voltage measurement unit    -   7 Current measurement unit    -   8 Battery    -   21 Fuel cell stack    -   21A Fuel cell    -   22 Electrolyte membrane    -   23 Fuel electrode    -   24 Oxidant electrode    -   25 Hydrogen supply unit    -   26 Oxygen supply unit    -   27 Separator    -   28 Hydrogen supply port    -   29 Oxygen discharge port    -   30 Hydrogen discharge port    -   31 Oxygen supply port    -   32 Fuel electrode side portion    -   33 Oxidant electrode side portion    -   34 Hydrogen inlet    -   35 Hydrogen outlet    -   36 Oxygen inlet    -   37 Oxygen outlet    -   38A Flow passage pattern    -   38B Flow passage pattern    -   39A Flow passage pattern    -   38B Flow passage pattern    -   41 Hydrogen supply source    -   41A Hydrogen tank    -   42 Hydrogen introduction passage    -   43 Hydrogen discharge passage    -   44 Three-way valve    -   45 Connection flow passage    -   46 Hydrogen pressure measurement unit    -   47 Valve    -   51 Oxygen supply source    -   51B Oxygen tank    -   52 Oxygen introduction passage    -   53 Oxygen discharge passage    -   54 Valve    -   55 Gas pressure measurement unit    -   56 Three-way valve    -   57 Circulation passage    -   58 Circulation pump    -   59 Pressure adjustment unit    -   60 Flow rate measurement unit    -   61 Condenser    -   62 Dehumidifier    -   63 Water recovery tank    -   71 Hydrogen coating unit    -   72 Hydrogen introduction unit    -   73 Capillary port    -   73 a Downstream tip end portion    -   73 b Upstream end portion    -   74 Purge port    -   75 Hydrogen discharge unit    -   76 Hydrogen supply side portion    -   76 a Groove    -   77 Neutron shielding member    -   78 Moisture absorption member    -   81 Temperature measurement unit    -   82 Temperature adjustment unit

1. A method of controlling a fuel cell device in which an electrolytemembrane is inserted between a fuel electrode and an oxidant electrode,hydrogen is supplied to a hydrogen supply unit of the fuel electrode,and a gas containing oxygen is supplied to a gas supply unit of theoxidant electrode so that power is generated, the method comprising: astep of supplying hydrogen to the hydrogen supply unit; a step ofmeasuring a voltage between the fuel electrode and the oxidant electrodeand determining whether the voltage is equal to or greater than areference voltage; and a step of discharging a gas containing oxygenfrom the supply unit to the outside while supplying the gas to the gassupply unit when the voltage is equal to or greater than the referencevoltage.
 2. The method of controlling the fuel cell device according toclaim 1, further comprising a step of depressurizing the hydrogen supplyunit of the fuel electrode and the gas supply unit of the oxidantelectrode when power generation of the fuel cell device is started,before the step of supplying the hydrogen to the hydrogen supply unit.3. The method of controlling the fuel cell device according to claim 1,further comprising a step of increasing current density of the fuel celldevice up to a predetermined value while performing conduction usingexternal resistance after the step of discharging the gas from the gassupply unit to the outside.
 4. The method of controlling the fuel celldevice according to claim 1, wherein a circulation passage capable ofconnecting a gas introduction passage of the gas supply unit to a gasdischarge passage is provided, and wherein the method further comprises:a step of determining whether impedance between the fuel electrode andthe oxidant electrode is equal to or less than a predetermined thresholdafter the step of supplying the gas containing oxygen to the gas supplyunit; and a step of connecting the gas introduction passage of the gassupply unit and the gas discharge passage via the circulation passage toform a circulation line and circulating the gas of the gas dischargepassage to the gas introduction passage when the impedance is equal toor less than the predetermined threshold.
 5. The method of controllingthe fuel cell device according to claim 4, further comprising: a step ofmeasuring a pressure difference between the hydrogen of the hydrogensupply unit and the gas of the gas supply unit and determining whetherthe pressure difference is greater than 0 and equal to or less than apredetermined threshold after the step of circulating the gas of the gasdischarge passage to the gas introduction passage, wherein a circulationamount of the gas is decreased when the pressured difference is greaterthan the predetermined threshold.
 6. The method of controlling the fuelcell device according to claim 4, wherein a circulation pump and adehumidifier are provided on the circulation line, and wherein the gasis circulated while being dehumidified in the circulation line in thestep of circulating the gas of the gas discharge passage to the gasintroduction passage.
 7. The method of controlling the fuel cell deviceaccording to claim 4, wherein a circulation pump is provided on thecirculation line and in the circulation passage, and wherein, in thestep of circulating the gas of the gas discharge passage to the gasintroduction passage, when the impedance is equal to or less than thepredetermined threshold, the circulation pump is activated in a state inwhich the gas is circulated from a gas supply source of the gas to theoutside via the gas introduction passage, the gas supply unit, and thegas discharge passage, and subsequently, the gas of the gas dischargepassage is circulated to the gas introduction passage by closing adischarge system discharging the gas from the gas discharge passage tothe outside.